Active Manipulation of Wave Propagation in Soft Periodic Structures

Author:Huang Yi Lan

Supervisor:zhang chun li chen wei qiu bao rong hao


Degree Year:2019





Phononic crystals(PnCs),the artificially structured materials with periodically arrayed unit cells,have been vastly researched in the recent several decades,due to their wonderful acoustic properties caused by the unique ability of manipulating wave propagation through band gaps.PnCs have shown the wonderful application prospects in novel acoustic devices,including sound filters,acoustic mirrors,acoustic wave guides,and vibration isolators.The acoustic properties of traditional PnCs keep nearly unchanged once the structure has been manufactured,inevitably limiting their applications in frequency-changing environments.Therefore,real-time modification of the properties of PnCs becomes a concern,giving rise to the concept of tunable PnCs.Soft hyperelastic materials can undergo large deformation repeatedly without causing any damage.Introducing large deformation into a periodic hyperelastic structure by applying a global mechanical loading can dramatically change its geometric configuration as well as the effective material properties,leading to an effective modification of band gaps in PnCs.In this thesis,several PnC structures made of soft materials are well studied,using commercial FEM software ABAQSUS with the secondary development scripts written in Python.Tunability of band gaps due to large deformation is thoroughly analyzed.Finally,several methods on wave manipulation are proposed.The main contributions are listed as follows:1)We design a square lattice PnC structure and a chiral lattice PnC structure.Post buckling deformation can be triggered in the square lattice structure,and its band structure can be modified.The post buckling deformation of the structure depends on the load pattern,which induces different buckling mode when it changes.On the other hand,the chiral lattice structure can undergo large deformation without buckling,due to the mirror symmetry being reduced by chirality.But band structure can also be manipulated very efficiently.In fact,large deformation without buckling is more stable and easier to control.2)A PnC plate made of soft material with resonant units is proposed.Each resonant unit consists of a mass which is connected to the perforated plate by thin beams.Obvious complete band gap is found to even exist in the intact structure without any mechanical loading.Results further show that remarkable tunability of band gaps with small pre-stretch is realized when strong resonance appears for some particular modes.In the proposed structure,the stiffness of the connecting beams can be substantially increased under a small pre-stretch.As a result,the resonance frequencies of the corresponding modes are increased,giving rise to a remarkable modification of the band gaps,while the geometry of the structure is nearly unchanged.3)We design a soft 1D PnC system by connecting two different periodic plates made of hyperelastic materials.By choosing different geometrical parameters of the two plates,topologically protected state of elastic waves is observed at the interface between them.Real-time shifting of the topological state can be realized by applying appropriate pre-stretch on the structure.The interface state wave modes can be either activated or deactivated by the pre-stretch applied on the structures with different initial geometrical parameters.Due to the advantageous property that topologically protected wave modes are stable against any defects and disorders,it provides a robust way of manipulating wave propagation in real time.